WASHINGTON (BLOOMBERG) - President Donald Trump on Wednesday (March 21) returned to criticisms of the special counsel investigating Russian election meddling.

He quoted former Harvard law professor Alan Dershowitz, who told Fox News on Friday that special counsel Robert Mueller never should have been appointed and that there was no evidence of a crime.

"Special Council (sic) is told to find crimes, whether crimes exist or not. I was opposed the the selection of Mueller to be Special Council, I still am opposed to it. I think President Trump was right when he said there never should have been a Special Council appointed," Trump said on Twitter, quoting Dershowitz.

In a subsequent message, Trump wrote, "there was no probable cause for believing that there was any crime, collusion or otherwise, or obstruction of justice!"

The tweets come as even Republicans in Washington have become concerned that Trump will fire Mueller, the former FBI director brought in as special counsel after Attorney General Jeff Sessions recused himself from investigating allegations of collusion between the Trump campaign and Russia.

Senate Majority Leader Mitch McConnell on Tuesday praised Mueller and said he should be allowed to finish his job, in his first comments since Trump began slamming Mueller over the weekend.

House Speaker Paul Ryan told reporters that Mueller should be allowed to complete his work.

Lawmakers took some comfort in statements from Trump attorney Ty Cobb and White House officials that Trump wasn't planning to oust Mueller.

But Trump continued to attack the investigation as a "witch hunt," and he hired Joseph diGenova, a former federal prosecutor who has said Trump is the victim of a "brazen plot" by the FBI and the Justice Department. DiGenova also has repeatedly criticised the Trump appointee who oversees Mueller's probe, Deputy Attorney General Rod Rosenstein.